Re: [PATCH] bpftool: Try to read btf as raw data if elf read fails

On Fri, Oct 18, 2019 at 03:39:05PM -0700, Jakub Kicinski wrote:

On Fri, 18 Oct 2019 12:34:04 +0200, Jiri Olsa wrote:

quoted

The bpftool interface stays the same, but now it's possible
to run it over BTF raw data, like:

  $ bpftool btf dump file /sys/kernel/btf/vmlinux
  libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
  [1] INT '(anon)' size=4 bits_offset=0 nr_bits=32 encoding=(none)
  [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
  [3] CONST '(anon)' type_id=2

I'm also adding err init to 0 because I was getting uninitialized
warnings from gcc.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/bpf/bpftool/btf.c | 47 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 9a9376d1d3df..100fb7e02329 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c

@@ -12,6 +12,9 @@
 #include <libbpf.h>
 #include <linux/btf.h>
 #include <linux/hashtable.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
 
 #include "btf.h"
 #include "json_writer.h"

@@ -388,6 +391,35 @@ static int dump_btf_c(const struct btf *btf,
 	return err;
 }
 
+static struct btf *btf__parse_raw(const char *file)
+{
+	struct btf *btf = ERR_PTR(-EINVAL);
+	__u8 *buf = NULL;

Please drop the inits

quoted

+	struct stat st;
+	FILE *f;
+
+	if (stat(file, &st))
+		return btf;

And return constants here

quoted

+	f = fopen(file, "rb");
+	if (!f)
+		return btf;

and here

quoted

+	buf = malloc(st.st_size);
+	if (!buf)
+		goto err;

and jump to the right place here.

quoted

+	if ((size_t) st.st_size != fread(buf, 1, st.st_size, f))
+		goto err;
+
+	btf = btf__new(buf, st.st_size);
+
+err:

The prefix for error labels which is shared with non-error path is exit_

quoted

+	free(buf);
+	fclose(f);
+	return btf;
+}
+

ok for all above

quoted

 static int do_dump(int argc, char **argv)
 {
 	struct btf *btf = NULL;

@@ -397,7 +429,7 @@ static int do_dump(int argc, char **argv)
 	__u32 btf_id = -1;
 	const char *src;
 	int fd = -1;
-	int err;
+	int err = 0;

This change looks unnecessary.

I'm getting confusing warnings from gcc about this,
but there is a code path where do_dump would return
untouched err:

  do_dump
     int err;

     } else if (is_prefix(src, "file")) {
       btf = btf__parse_elf(*argv, NULL);   // succeeds

     }

     while (argc) {
       if (is_prefix(*argv, "format")) {
       else {                                // in here
          goto done;
       }

     done:
       return err;

thanks,
jirka